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NSN probably means Nato Stock Number. If so, the numerals following are ....
its Nato Stock Number, which can be used to identify what it is. Does it look like a military piece of kit? If so, one of our military nutz can probably get a colleague to look it up.
The -21 indicates a Canadian Forces part. That's all I can tell you. You need access to the CF parts database to get the other information I'm afraid. If there's a CF logistics tech on this board, he/she may be able to help out.